It is known that the marketing of bottled wines requires not only that the wine be clear at the time of bottling but that it remain so for a period of time, especially so in the case of wines which are stored for relatively long periods of time.
Now, it is known that current wine stabilization treatments are not very satisfactory, whether this is in regard to precipitations of tartaric salts or those of proteins, referred to in the field of oenology as "tartaric and proteinic spoilage".
In fact, during the storage of white wines, proteinic spoilage results in cloudiness or specific deposits which appear in the bottle when the storage temperature of the wine is elevated and/or as a result of the wine being enriched with the tannins from the cork.
A known solution involves treating the musts and the wines with bentonite, but the dosages necessary in terms of the requirements may be sufficiently high to detract from the organoleptic characteristics of the wines thus treated.
Other attempts were made along enzymatic lines, using exogenic proteases, or on the basis of yeast, in order to eliminate the proteins responsible for the proteinic spoilage, but the results were not satisfactory.
It was recently shown by the inventors of the present application that, in the course of the storage of white wines on the lees, the noted improvement of the proteinic stability of white wines was due to the presence of mannoproteins released by the yeasts.
With regard to the precipitation of tartaric salts, which are present essentially in the form of potassium acid tartrate, they are in a state of supersaturation in the wines. In addition, during storage of the wine in winter, the cold causes crystalline precipitations, but in any event this precipitation also occurs in the course of time and is visible in the bottles.
Ways in which to stabilize these tartaric salts have been sought and at present three are known.
The first solution involves accelerating the precipitation by maintaining the wine for a number of weeks at negative temperatures, then filtering the wine to withdraw the crystals.
The second solution involves improving on the first solution, by adding elevated doses of crystals to the wine such that the low temperature treatment is rendered more effective and its duration is shorter, but filtration remaining obligatory in order to withdraw the additional crystals and the crystals which have developed.
The third solution involves the addition of mesotartaric acid to the wine, which acid counteracts the crystallization of the tartaric acids under the low temperature effects. The protective effect disappears as soon as the mesotartaric acid hydrolizes, which takes place all the more rapidly the higher the storage temperature of the wine.
These solutions are not satisfactory, because the first two are lengthy and costly in addition to altering the organoleptic characteristics of the wine treated.
With regard to the third solution, its effectiveness is of short duration, and is therefore restricted to wines intended for early consumption, in addition to the fact that it is necessary to introduce into the wine a foreign compound which is initially not contained therein.
More recent tests have shown that the mannoproteins extracted under heat from the cell walls of the yeast belonging to the species Saccharomyces cerevisiae have an inhibitive effect on the crystallization of tartaric salts.
The process to obtain'these mannoproteins involves rendering them soluble with heat at 100.degree. C. in an aqueous medium and to collect them, either directly by lyophilization, or by precipitation with ethanol and by drying the precipitate after centrifugation.
Yet, the effectiveness of the proposed preparations when tested in a model medium was not verified in respect of the majority of wines. Moreover, said preparation of mannoproteins does not contribute any improvement to the proteinic instability of white wines.